Dry dock pontoon providing improved stability

ABSTRACT

In the multi-section dry dock construction disclosed herein, the pontoon portion of each section is subdivided by watertight bulkheads in a pattern which improves lateral stability and provides flexibility in longitudinal loading capability while retaining a basically easily pumped and drained arrangement. In one embodiment, each side of the pontoon is divided into three watertight compartments, two of which are L-shaped and are arranged in complementary fashion with the third compartment enclosed therebetween. The bases of the L-shaped compartments are adjacent the center line of the pontoon so that all three compartments extend under a respective one of the dry dock wings and may therefore be easily pumped.

United States Patent 1 [111 3,709,177 Crandall 1 Jan. 9, 1973 [541 DRY DOCK PONTOON PROVIDING IMPROVED STABILITY Primary Examiner-Milton Buchler Assistant Examiner-Gregory W. O'Connor Attorney-Kenway, Jenney & Hildreth [57] ABSTRACT In the multi-section dry dock construction disclosed herein, the pontoon portion of each section is subdivided by watertight bulkheads in a pattern which improves lateral stability and provides flexibility in longitudinal loading capability while retaining a basically easily pumped and drained arrangement. In one embodiment, each side of the pontoon is divided into three watertight compartments, two of which are L- shaped and are arranged in complementary fashion with the third compartment enclosed therebetween. The bases of the L-shaped compartments are adjacent the center line of the pontoon so that all three compartments extend under a respective one of the dry dock wings and may therefore be easily pumped.

4 Claims, 6 Drawing Figures f ""TZF' l i r i I i l i i i 1 i i i i i i i l l 4 l l l l l i i 434A i i i i l 35- 1 36- :37 pslh i I l 1 I i i i i l :l':t-+l Will" I 39 ea 34 :36A- i as? 1 I 1 A 1 I 1 1 I l I I I q PATENTEUJAH 9 I973 SHEET 1 [IF 3 FIG. 2

INVENTOR PAUL S. CRANDALL BY we? ATTORNEYS PATENTEDJAN 9 I973 SHEET 2 BF 3 FIG. 3

LLLLLLL rrrrrrrrrrrrrl rrrfirrrflr INVENTOR PAUL S. CRANDALL ATTORNEYS DRY DOCK PONTOON PROVIDING IMPROVED STABILITY BACKGROUND OF THE INVENTION comprises a pair of wings which rise vertically along the sides of the section and a generally horizontal pontoon part which extends between the bottoms ofv the two wings. In the operation of such a dry dock, a critical phase occurs just as the upper surface of the pontoon portions are awash during raising and lowering of the dock with a capacity vessel. When the dry dock is fully pumped out, whether loaded or unloaded, it is relatively stable since the entire area of each pontoon contributes to the righting moment which resists any listing. However, as the upper deck of the pontoon portion becomes submerged during lowering of the dry clock, a righting moment is provided only by the wing areas. Further, at this point, the combined center of gravity of the dry dock, together with the load of any ship held therein and interior ballast water, is relatively high. Further submergence of the dry dock both lowers the combined center of gravity and tends to immerse the hull of the ship contained in the dry clock so that the ships inherent stability aids the stability of the dry dock.

Among the several objects of the present invention may be noted the provision of a dry dock construction providing improved lateral stability; the provision of such a dry dock construction which particularly provides increased stability during the raising and lowering of the dry dock; the provision of such a construction which permits efficient pumping and draining of the dry dock; the provision of such a construction which permits flexibility in the loading of each section of a multi-section dry dock; the provision of such a con- 7 struction which is highly reliable and which is relatively simple and inexpensive. Other objects and features will be in part apparent and in part pointed out hereinafter.

SUMMARY OF THE INVENTION Briefly, a dry dock constructed in accordance with the present invention comprises a plurality of sections each of which includes a skin or shell providing a pair of wings and a pontoon extending therebetween. A central, longitudinally extending watertight bulkhead divides the pontoon portion into a pair of side sections. Further watertight bulkheads are provided which divide each of the side sections into three compartments, two of which are L-shaped and are arranged in complementary fashion with the third compartment, which is of generally rectangular shape, being between the uprights of the Ls. The bases of the Ls are adjacent the central longitudinal bulkhead so that each compartment extends to the respective wing. A respective pump is provided for each compartment, located substantially beneath the respective wing.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a somewhat diagrammatic illustration, in perspective, of a multi-section dry dock, together with a ship load, employing a plurality of individual sections constructed in accordance with the present invention;

FIG. 2 is a sectional plan view of one side of one of the dry dock sections shown in FIG. 1;

FIG. 3 is a sectional view taken substantially on the line 33 of FIG. 2;

FIG. 4 is a sectional view taken substantially on the line 4-4 of FIG. 2;

FIG. 5 is a sectional view taken substantially on the line 55 of FIG. 3; and

FIG. 6 is a sectional plan view, similar to FIG. 2, of another embodiment of a dry dock section constructed in accordance with the invention.

Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, there is indicated at 11 generally, a dry dock constructed in accordance with the present invention, together with a ship load 13 held in the dry dock. As illustrated, dry dock 11 comprises five similar sections 14-18, each comprising its own watertight skin or shell of steel plate. As has been provided heretofore, the individual sections 14-18 may be separated and/or assembled in different numbers to facilitate repair and maintenance of individual sections as needed.

Taking the first section 14 as an example, it may be noted that each section comprises a pair of upright wings 21 and 23 which are connected at their lower ends by a generally horizontal pontoon portion 25. As is conventional, the ship 13 is brought in between the wings 21-23 while the dry dock is submerged to such an extent that the upper deck of the pontoon 25 is lower that the draft of the ship 13. Then the individual sections 14-18 are pumped out to raise the ship for servicing and/or maintenance. Typically, the dry dock will be raised to such an extent that the upper deck of each pontoon is above water level, the boat 13 being supported on suitable blocks or a cradle.

FIG. 2 indicates the general internal layout of each pontoon 25. The interior of the pontoon includes a plurality of transverse bulkheads 33-39. Throughout this specification the term transverse" is used in the sense of meaning transverse to the longitudinal axis of the entire dry dock construction. a

The bulkheads 33-39 extend fully between the upper deck and bottom of the pontoon so as to form with these plates a lateral box girder of tremendous strength. This strength allows a ship load, concentrated along the center line of the dry dock, to be borne by a buoyancy applied to all or part of the area of the pontoons 25 without deforming the pontoons.

As noted previously, it is conventional to divide the pontoon portion of each section by means of a central longitudinal watertight bulkhead. Such a bulkhead is indicated at 31 in FIG. 2 which illustrates the general internal layout of the pontoon. In FIG. 2, bulkheads or portions of bulkheads which are watertight are indicated by double lines while non-watertight bulkheads, provided for structural strength, are indicated by single lines. Portions of the bulkheads 34, 36 and 38 are watertight as indicated by the double lines in FIG. 2, these watertight portions being designated 34A, 36A and 38A, respectively. The interior of the pontoon 25 also includes a longitudinal watertight partition 40 which links the watertight partition portions 34A, 36A and 38A. Each side of the pontoon 25 is thus divided into three watertight compartments, designated I, II and III,

As may be seen, the compartments I and II are generally of L-shaped configuration, the Us being oriented in complementary fashion so that the remaining compartment III, which is of generally rectangular configuration, is enclosed between the upright portions of the Us. The base portions of the L-shaped compartments I and II abut one another and are adjacent the central longitudinal partition 31 and thus all three compartments I, II and III extend under the respective wing 21. A separate pump is provided for each of the three compartments. In FIG. 2 these pump locations are indicated at 41, 42 and 43.

The interior construction of the pontoon may be seen in greater detail in FIGS. 3-5. As noted previously, the transverse bulkheads 33-39 extend as webs between the pontoon deck, designated 45, and the bottom plate of the pontoon, designated 47. Between the bulkheads 33-39, the deck ,and bottom plates 45 and 47 are stiffened by scantlings, designated 51, which run parallel to the bulkheads 33-39, that is, transverse to the longitudinal axis of the dry dock. The scantlings 51 are, in turn, backed up by girts 53 which extend between the transverse bulkheads. As is conventional in such construction, welding is the preferred form of attachment. A similar stiffening system is also provided by the rest of the steel plate shell forming each pontoon and for the various watertight bulkheads though these scantlings and girts have been omitted from the drawings to avoid obscuring the overall arrangement according to the invention.

As the scantlings are themselves directly adjacent the bottom plate 47 and run transversely of the dry dock, they form a natural water course for water being drained from the compartments 1, II and III by the pumps 41, 42 and 43 with regard to lateral flow of such water from the central portions of each dry dock section 14-18.

A longitudinal depressed waterway 61, stiffened by longitudinally extending scantlings 63 is provided along each outer edge of the pontoon portion for facilitating a flow from between the various transverse scantlings 51 to the respective pump within each watertight compartment I, II and III. Each pump, e.g.,. that indicated at 41 in FIG. 3, is driven, through a shaft 65 by a respective motor 67 located well up in the respective wing 21 or 23. Preferably, each pump outlet is also provided with a shutoff valve 69 and a flooding valve 70 which can be operated from above in the wing, as illustrated.

In the base of the L in each of the compartments I and II, the transverse scantlings 51 terminate short of the longitudinal watertight partition 40, as illustrated in FIG. 4, and longitudinal scantlings 71 are used adjacent this watertight partition so as to lead water from the base portions of the L-shaped compartments I and II around the compartment III, without having to flow over any scantling. As illustrated in FIG. 4, the nonwatertight portions of the transverse bulkheads, such as 35, may include access openings at 73 so as to permit the passage of workmen between the spaces separated by bulkheads in each watertight compartment. Thus, only one access port (not shown) from the wing needs to be provided for each compartment I, II and III.

While each of the compartments I, II and III extends under the respective wing, the centers of buoyancy of the compartments I and II are relatively inboard whereas the center of buoyancy of the compartment III is relatively outboard. Since these three compartments are separated by watertight bulkheads so that there is no common water plane between them, it can be seen that the lateral stability of the dry dock section is substantially improved. Such improvement, however, is not obtained at the expense of pumping ease and efficiency nor at the expense of mechanical strength or integrity. Each of the compartments I, II and III can be emptied by means of a pump located directly beneath the wing so that pump servicing, if required, is relatively easy. Further, water flow to each pump is substantially along the bottom plate of the pontoon itself and is relatively free and open. In FIG. 2,the path of water flow is indicated generally by the broken line arrows. Thus, substantially no inlet piping to the pumps is required. Since the flow of water along the floor is relatively unimpeded between the scantlings, the entire pontoon may be pumped essentially dry before the pump will break suction. Thus, substantially the entire theoretical displacement of the dry dock shell may be utilized in lifting the weight of the dry dock together, with its load. Since the compartments I, II and III are of substantially equal area as shown in FIG. 2,-it can be seen that the pontoon will tend to lift equally, assuming equal capacities ofthe pumps 41-43.

A further advantage of the relatively free drainage of liquid from the several compartments I, II and III along the bottom plate of the dry dock is that accumulations of mud and sludge can be relatively easily washed down out of the compartments so that they will be picked up and ejected by the pumps. Thus, the efficiency of the dry dock will not be impaired by essentially permanent accumulations of foreign material which reduce the effective working displacement of the dry dock, as in some contemporary arrangements.

While the drainage of each of the compartments is .relatively free and open, this drainage has been obtained by coordinating the compartmenting function with a strong bulkheading and local reinforcement system so that great structural strength and integrity are inherently provided. TI-Ie particular arrangement illustrated is also advantageous in that it is essentially a lay-on type of construction in which the dry dock can be built from the bottom up, that is, piece can be laid upon piece and welded togetherwith relatively little interfitting or requirement of pre-assembly. Thus, conventional shipyard and welding techniques are readily adaptable.

A further advantage of compartmenting in accordance with the present invention is that the buoyancy of each individual dry dock section 14-18 can be adjusted to accommodate a loading which is not centered in the fore and aft direction. For example, in the situation illustrated in FIG. 1, the blocking under the stern of the ship 13 may cause loading to be applied essentially only at the forward end of the section 14.v By pumping differentially, that is, by removing water faster from compartment II than from .compartment I, a differential in buoyancy can be built up so as to at least partially counteract this moment, which would otherwise place strains on the couplings between the several dry dock sections 14-18.

While the arrangement illustrated in FIGS. 1-5 is preferred, a topologically related variation is also possible. This variation is illustrated, somewhat diagrammatically, in FIG. 6 which corresponds to FIG. 2 of the original embodiment. In the FIG. 6 variation, the pontoon 25 is again divided into three compartments, designated IV, V and VI, which are of equal area. In this variation, however, one of the compartments (IV) is of a T-shaped configuration and the other two compartments V and VI are of generally rectangular shape and are nested on either side of the T-shaped compartment. The cross-bar of the T-shaped compartment IV is adjacent the longitudinal center line' of the dry clock so that, again, all three compartments extend under the wing on the respective side. In one sense the variation of FIG. 6 can be seen to be essentially equivalent to splitting the embodiment of FIG. 2, fore and aft and then re-assembling the halves in the opposite order.

Assuming a mode of construction analogous to that described with reference to the first embodiment, it can be seen that the variation of FIG. 6 will likewise provide relatively free draining of all three compartments to the vicinity of the wing where pumping can be relatively easily provided. In FIG. 6, pump locations are indicated at 74, 75 and 76 and the flow pattern is again indicated by broken line arrows. In this variation, the center of buoyancy of the T-shaped compartment IV is relatively inboard while the centers of buoyancy of the compartments V and VI are relatively outboard. Thus, this arrangement will also provide an improvement in lateral stability during the critical period when the deck ofthe pontoon isjust awash.

The watertight compartments of either embodiment can also be further subdivided. Preferably, this subdivision is performed in a symmetrical manner, e.g., by dividing the T-shaped compartment IV of the FIG. 6 embodiment into two L-shaped compartments or by dividing the rectangular compartment III (FIG. 2) down the bulkhead 36. In either case, four compartments are obtained, facilitating the use of four pumps for faster pumping. As with the original embodiments, it is desirable that all of the compartments be of equal area. Such arrangements may be preferable in the construction of relatively large dry docks, e.g., over 70,000 tons capacity.

In view of the foregoing, it may be seen that several objects of the present invention are achieved and other advantageous results have been attained.

As various changes could be made in the above constructions without departing from the scope of the invention, it should be understood that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is: l. A dry dock section comprising: a shell providing a pair of wings and a pontoon; a central longitudinal watertight bulkhead dividing said pontoon into a pair of side sections; watertight bulkheads dividing each of said side sections into three compartments two of which are L- shaped and are arranged in complementary fashion with the third compartment being between the uprights of the Ls and being of generally rectan -ular sharge, said central bulkhead defining one e ge of the ase of each L, the three compart- 'ments in each side section extending under the respective wing; and

a respective pump for each compartment located substantially beneath the respective wing.

2. A dry dock section comprising:

a shell providing a pair of wings and a pontoon;

a central longitudinal watertight bulkhead dividing said pontoon into a pair of side sections;

a plurality of transverse bulkheads in each side section extending between the deck and bottom of said pontoon and forming therewith a transverse box girder;

a watertight longitudinal bulkhead in each side section linking selected ones of said transverse bulk heads and therewith dividing each side section into three watertight compartments, two of which are L-shaped and are arranged in complementary fashion with the bases of the Ls abutting and with the third compartment being between the uprights of Ls and being of generally rectangular shape, said central bulkhead defining one edge of the base of each L, the three compartments in each side section extending under the respective wing; and

a respective pump for each compartment located substantially beneath the respective wing.

3. A dry dock section as set forth in claim 2 including a plurality of scantlings supporting the bottom of said pontoon and extending parallel to said transverse bulkheads, and including also a plurality of girts supporting said scantlings and extending between adjacent pairs of said transverse bulkheads.

4. A dry dock section as set forth in claim 3 including a depressed longitudinal waterway running under each wing in each compartment for collecting water flowing from between the transverse scantlings in the respective compartment. 

1. A dry dock section comprising: a shell providing a pair of wings and a pontoon; a central longitudinal watertight bulkhead dividing said pontoon into a pair of side sections; watertight bulkheads dividing each of said side sections into three compartments two of which are L-shaped and are arranged in complementary fashion with the third compartment being between the uprights of the Ls and being of generally rectangular shape, said central bulkhead defining one edge of the base of each L, the three compartments in each side section extending under the respective wing; and a respective pump for each compartment located substantially beneath the respective wing.
 2. A dry dock section comprising: a shell providing a pair of wings and a pontoon; a central longitudinal watertight bulkhead dividing said pontoon into a pair of side sections; a plurality of transverse bulkheads in each side section extending between the deck and bottom of said pontoon and forming therewith a transverse box girder; a watertight longitudinal bulkhead in each side section linking selected ones of said transverse bulkheads and therewith dividing each side section into three watertight compartments, two of which are L-shaped and are arranged in complementary fashion with the bases of the Ls abutting and with the third compartment being between the uprights of Ls and being of generally rectangular shape, said central bulkhead defining one edge of the base of each L, the three compartments in each side section extending under the respective wing; and a respective pump for each compartment located substantially beneath the respective wing.
 3. A dry dock section as set forth in claim 2 including a plurality of scantlings supporting the bottom of said pontoon and extending parallel to said transverse bulkheads, and including also a plurality of girts supporting said scantlings and extending between adjacent pairs of said transverse bulkheads.
 4. A dry dock section as set forth in claim 3 including a depressed longitudinal waterway running under each wing in each compartment for collecting water flowing from between the transverse scantlings in the respective compartment. 